Tuned liquid dampers are well known to the person skilled in the art and are discussed in general textbooks which deal with the dissipation of vibration energy present in structures. The tuned liquid dampers known in the prior art are typically either rectangular or cylindrical tanks. Rectangular TLDs are typically used on buildings with a rectangular cross section and cylindrical TLDs are typically used on structures with a square or circular cross section.
A first example is US 2005/0050809 A1 which discloses a rectangular TLD which is located on the top floor of a tall building and which is used for dampening the vibrations of the building. U.S. Pat. No. 5,560,161 describes a more advanced TLD where the motion of the water in the tank is actively controlled in order to better control the damping characteristics of the damper.
However, it has been discovered that the rectangular and cylindrical tuned liquid dampers have a number of disadvantages. For the first, it can be shown that a significant portion of the liquid in a rectangular or cylindrical liquid damper does not move during the motion of the structure and it therefore does not contribute to the damping effect of the TLD. In other words, the “participation mass” of the liquid is quite low. The rectangular and cylindrical liquid dampers are therefore quite heavy since a large amount of liquid is required to obtain the desired damping effect. Furthermore, the rectangular and cylindrical tuned liquid dampers do not work well for rotational vibrations. In addition, rectangular and cylinder TLDs do not work in situations where the TLD is exposed to large angular motions or in cases where proper alignment of the TLD is difficult to achieve.
As a side note, we note that JP 2000249186 A shows a device which is similar in appearance to the device of the current invention, but which has an entirely different purpose. The device disclosed by JP 2000249186 A is of the “Lancaster Damper” type and is not considered to be a tuned liquid damper. The damping action of a Lancaster damper device is due to the viscous friction present between two moving objects separated by a viscous fluid. JP 2000249186 A discloses a device where a spherical element is floated inside a spherical housing. A viscous fluid is located in a small gap between the outer spherical housing and the floating inner spherical element. Due to the inertia of the inner object, when the outer housing is rotated, the inner object tends to stay still. Viscous friction therefore occurs between the inner object and the outer housing. This viscous friction allows this device to be used to dampen rotational movements. There is however no damping effect for translational vibrations.
We also note that an article published in 1982 by Sayar and Baumgarten disclosed a spherical container partially filled with a liquid being used as a slosh damper. The full reference to the article is Bashir A. Sayar and J. R. Baumgarten: Linear and Nonlinear Analysis of Fluid Slosh Dampers, AIAA Journal, November 1982, Vol. 20, No. 11, pp. 1534-1538. However, it has not been possible to find other references showing the use of liquid slosh dampers with spherical housings. It seems therefore that the person skilled in the art at the time of writing, did not recognize the advantages of a spherical tuned liquid damper. The spherical housing was most likely used in the above mentioned article due to the research available at the time on the motion of fuel in spherical fuel tanks installed on space ships and satellites.